Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006a%26a...453l..25g&link_type=abstract
Astronomy and Astrophysics, Volume 453, Issue 2, July II 2006, pp.L25-L28
Astronomy and Astrophysics
Astrophysics
17
Galaxies: Individual: Ngc 2997, Galaxies: Spiral, Galaxies: Star Clusters, Galaxies: Structure, Infrared: Galaxies, Techniques: Spectroscopic
Scientific paper
Context.Many grand design spiral galaxies show strings of bright knots along their arms on near-infrared K-band images. The alignment of such knots suggests a relation to the spiral pattern and possibly to a large-scale, star-forming front associated with a density wave. Aims.Bright knots in the southern arm of NGC 2997 were studied to determine their nature and evolutionary state.Methods.Low resolution near-infrared K- and J-band spectra of the knots were observed with ISAAC on the VLT. Results.Most of the knots show strong H I Brγ emission with some also having He I and H2 emission. A few knots show indications of 12CO absorption. This suggests that the knots are very young stellar clusters with masses up to 5×104 M&sun;.Conclusions.The knots azimuthal distance from the K-band spiral correlates well with their Brγ strength, indicating that they are located inside the co-rotation of the density wave, which triggered them through a large-scale, star-forming front. These relative azimuthal distances suggest an age spread of more than 1.6 Myr, which is incompatible with standard models for an instantaneous star burst. This indicates a more complex star-formation history, such as several bursts or continuous formation.
Dottori Horacio
Gredel Roland
Grosbøl Preben
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